Inverters are circuits for converting a direct current (DC) to an alternating current (AC). That is, an inverter converts direct current electric energy from a source, such as a battery, to an alternating current, which is generally a sine wave or square wave. One particular type of inverter is a multi-level inverter that is configured to first convert a direct current into a step-like square wave of multiple levels, and then form a sine wave by using a filter. If there are more levels implemented by the multi-level inverter, a waveform of a sine wave that is obtained by the multi-level inverter is more approximate to a standard sine waveform. Multi-level inverters are a common power topology for high and medium power applications such as utility interfaces for renewable power sources, flexible alternating current transmission systems, medium voltage motor drive systems, and the like.
In terms of topology varieties, multi-level inverters take many forms, such as diode-clamped multi-level inverters, flying capacitor multi-level inverters, and others (e.g. cascaded H-bridge multi-level inverters, etc.). Unlike flying capacitor multi-level inverters which typically employ capacitors for clamping purposes, diode-clamped multi-level inverters use diodes to provide multiple voltage levels through different phases to capacitor banks. In use, the diode transfers a limited amount of voltage, thereby reducing the stress on other electrical componentry.
Diode-clamped multi-level inverters, however, are limited in a variety of ways. For example, by virtue of the passive nature of the diode(s) themselves, a modulation scheme that controls inverter operation is limited. Further, diode-clamped multi-level inverters are often void of the topology features of other types of topology-specific features (e.g. flying capacitors, etc.) that may afford beneficial attributes in certain topological configurations. Even still, in the event additional levels are desired, diode-clamped multi-level inverter topologies require a significant number of additional components that is directly proportional to the number of desired additional levels. In addition to the augmented cost resulting from such extra required components, there are operational considerations, as well. For instance, the more components incorporated at each inverter level results in larger loop inductances which, in turn, can frustrate switching at high rates (e.g. tens of kHz, etc.).